Driver's licence

Here are some suggestions.  If you need to maintain a residence in a particular state get an account with a National Mail Forwarding company like Mail Box etc, or a reliable relative. Many full time RV travelers use their P.O box as a residential address by prefixing the APT in front of the box number.  This allow you to use that address for Tax info, License, Bank ETC.

This service will open your mail, scan, and email it to you, then shred your documents. http://www.earthclassmail.com/ 
They are Oregon based so if you need an address in your state you'll need a service in that state. Many forward form the state service to Oregon. Getting mail via email with attached PDF files is more reliable than mail in non US countries.  Tennessee is a state that will allow you to renew your license by mail but requires in state delivery of renewal notices. If your state does not allow renewal by mail then you will need to plan on returning to the states during renewal period.

TIP: Do not do a postal change of address to the in state forwarding service address.  You do not need junk mail just do a change of address directly with the vendors like your bank, state, etc.  You have to pay for the shipping of all documents forwarded so only the nitty gritty.

Also check directly with your state licensing division they may already have a policy in place to handle your issue. I would see if I could talk to an Attorney that specializes in overseas travel and residences. I'm sure there are several options knowing the pro's and con's before hand is best. The State Department also has information, either download or order the documents on living aboard.  Hope I help steer you in the right direction.